Caramel color is a product of the heat treatment of carbohydrates, typically sugars, usually in the presence of a catalyst. There are several types of caramel colors, for example, non-acid resistant and acid resistant types. The different types of caramel colors are chosen for their suitability for a particular end use. With soft drinks, acid-resistant type caramel colors are required. Malt beverages such as beer require non-acid resistant caramel color. Non-acid resistant caramel color particularly suitable for malt beverages is produced using an aqueous ammonia or anhydrous ammonia catalyst. This is referred to as ammonia caramel color.
Ammonia caramel color is generally produced using a batch type process. In a batch type process a large kettle containing up to 2000 gallons or more of a carbohydrate syrup such as corn syrup is heated to boiling for about 8 to 12 hours at atmospheric pressure. Gradually the ammonia catalyst is added and the color forms. This is then slowly cooled and filtered and brought to the desired concentration.
Current batch processes are very slow usually requiring 8-12 hours or more. Increasing the temperature of the batch reaction will increase the rate, however increased pressure is required. When producing ammonia caramel color the increased pressure causes hazing of the caramel and eliminates beer stability thereby providing an unacceptable caramel color. Beer stability refers to the tendency of the caramel color to remain dissolved in beer and not cause the beer to become murky.
Another problem with caramel color is the production of 4-methyl imidazole (hereafter 4MeI) and 2-acetyl-4(5)-tetrahydroxy butyl imidazole (hereinafter THI). Over the past several years the Food and Drug Administration has limited the content of 4MeI in caramel color and may soon limit the THI content. It is believed that 4MeI and THI are reaction products of the carbohydrate in combination with the ammonia catalyst. To control the production of 4MeI and THI the ammonia catalyst must be added to the batch reactor very slowly. This is particularly difficult to control accurately; and even with this slow addition of the ammonia catalyst, unacceptably high levels of 4MeI and THI are sometimes encountered. Such high levels can require discarding of an entire batch of caramel color. THI and 4MeI content is even more of a problem with a darker caramel color is desired. The darker color is produced by more severe reaction condition which tend to increase THI and 4MeI.
Salt stability is also a concern with caramel color which is added to certain food products. Salt stable caramel color does not precipitate or turn turbid when added to a concentrated salt solution. Dark caramel color is rarely salt stable.
Although apparently never commercially developed, methods have been disclosed to produce caramel color under high pressure. For example, Meisel U.S. Pat. No. 3,214,294 and Ackermann U.S. Pat. No. 3,385,733 disclose continuous high pressure methods of producing caramel colorings. The Ackermann reference teaches forming a mixture of catalyst and carbohydrate syrup preferably corn syrup, preheating this to a temperature of 350.degree. F. to 1,000.degree. F., maintaining this reaction mixture in a continuous reactor under pressure for a period of 5 to 300 minutes. Various catalysts including phosphoric and sulfuric acids and ammonium, potassium or sodium hydroxide are disclosed. Meisel also discloses using ammonium bisulfite as a catalyst.
Ammonia caramel produced according to the teachings of Meisel or Ackermann would have excessively high 4MeI and THI contents and further hazing would occur causing an unacceptably cloudy product.